1. Field of the Invention
This invention relates to an improvement in a valve operation changing system for changing the valve timings of an intake or exhaust valve of an internal combustion engine in accordance with engine operating conditions.
2. Description of the Prior Art
Valve operation changing systems have been applied to various uses in the field of internal combustion engines. For example, a valve operation changing system is used in a dual-mode engine which is so arranged that the valve timing of the intake and exhaust valve is changed at a light load engine operating range so as to deactivate some cylinders, thereby carrying out a part-load engine operation.
In general, a gasoline engine of the type wherein charge is previously prepared by mixing air and fuel has a tendency that good fuel economy is obtained at a high engine load operating range. In this regard, in the dual-mode engine, the intake and exhaust valves of some cylinders are kept fully closed to interrupt the supply of air and fuel thereinto thereby to de-activate the cylinders. This relatively increases engine load applied to the remaining cylinders, thereby improving fuel economy of the engine at the light load engine operating range.
The valve timing changing of the intake and exhaust valves of the dual-mode engine is usually carried out by transferring rocker arms from a first cam for cylinder activation or working onto a second cam for cylinder deactivation or rest in accordance with the engine operating conditions. The first and second cams are formed on a single camshaft and located side by side.
In order to thus transfer the rocker arms, the rocker arm axial moving distance must be longer than the width of each cam. Accordingly, it is required that an actuator device for driving the rocker arms have a longer moving stroke and a larger driving force for the purpose of achieving smooth and reliable transfer of the rocker arms.